1. Field of the Invention
The invention relates to an electrode line for an implantable cardiac stimulator for delivering electrical stimulation pulses for therapy of a heart, e.g., cardial resynchronization therapy (CRT) of a heart, as well as such a cardiac stimulator itself. The cardiac stimulator may be a cardiac pacemaker or an implantable cardioverter/defibrillator (ICD) or a combination of both, which is capable of stimulating both ventricles of a heart.
2. Description of the Related Art
A cardiac stimulator of this type typically has at least one right-ventricular sensing unit and one right-ventricular stimulation unit as well as one left-ventricular sensing unit and one left-ventricular stimulation unit. These units are each connected in operation of the cardiac stimulator via electrode lines to electrodes to be implanted at suitable points in the heart. The electrode line having the electrodes for detecting electrical potentials in the left ventricle of the heart and for delivering left-ventricular stimulation pulses are typically a component of a left-ventricular electrode line, which is laid through the coronary sinus of a heart and is therefore also referred to as a coronary sinus electrode line. The electrodes for detecting electrical potentials in the right ventricle and for delivering right-ventricular stimulation pulses are typically fastened to a right-ventricular electrode line whose distal end extends up into the apex of the right ventricle. The electrode lines are typically connected at their proximal end via standardized plug connections to a corresponding cardiac stimulator.
The typical stimulation modes of a right-ventricular cardiac stimulator, such as VVI, VVD, or DDD, may be presumed to be known. This is also true for the delivery of stimulation pulses only in case of demand (demand pacemaker), in which the delivery of a stimulation pulse to a particular chamber of a heart is suppressed if a particular intrinsic action (intrinsic contraction) of the particular ventricle was previously detected in a corresponding escape interval via a sensing unit of the cardiac stimulator assigned to this ventricle. These concepts, which are known per se, may also be implemented in the cardiac stimulator described here.
The cardiac stimulator discussed here is preferably a biventricular cardiac stimulator which is fundamentally capable of stimulating both ventricles of the heart continuously or on demand.
In particular for cardiac stimulators of this type, the need exists to adapt the particular therapy as well as possible to the particular hemodynamic status of the patient.
Currently, various methods for detecting the hemodynamics are being researched. Either direct methods of pressure measurement in the pulmonary vein, left atrium, or ventricle are studied here, or indirect methods of impedance cardiography are being pursued. The methods of pressure measurement have the disadvantage that additional sensors are implanted in the heart. These sensors require an increased effort during implantation, because the desired implantation locations differ from the standard electrodes (ICD and pacemaker).
The impedance-based methods have the disadvantage that the hemodynamic variables may only be derived indirectly here and thus the disadvantage of replicability exists. The question always arises as to whether the physician believes in these methods.
Integrating an acceleration sensor (accelerometer) in intracardial electrode line, which provides information about the movement of the electrode line, which correlates to a certain degree with the movement of a particular heart part, see, for example, US 2004/0172078, US 2004/0172079, and US 2005/0027320, has already been suggested. Furthermore, in “An Implantable Intracardiac Accelerometer for Monitoring Myocardial Contractility”, Pacing and Clinical Electrophysiology 19 (12), pages 2066-2071, a direction-independent application of an accelerometer integrated in the electrode has been described. In spite of the results, which were already published in 1996, up to this point there has been no successful commercial usage of the concept.